Multi-channel radiofrequency receiver

ABSTRACT

The invention relates to a multichannel radio-frequency receiver ( 1 ) for electromagnetic waves, having a radio-frequency analogue section ( 2 ) which has an input ( 3 ) for an electrical signal of a receiving device ( 4 ), and having an lower-frequency section ( 8, 9 ) which is connected downstream from the radio-frequency analogue section ( 2 ) and has a plurality of parallel channels ( 6   b   , 6   c   ; 7   b   , 7   c ) for respectively different signal strengths and an evaluation circuit, in which a signal divider ( 5 ) is provided in the radio-frequency analogue section ( 2 ) in order to split the signal in accordance with a predeterminable division ratio into signal elements which can be supplied to radio-frequency analogue channels ( 6   a   , 7   a ), downstream from which the channels ( 6   b   , 6   c   ; 7   b   , 7   c ) of the lower-frequency section ( 8, 9 ) are respectively connected, and the channels ( 6   b   , 6   c   ; 7   b   , 7   c ) of the lower-frequency section ( 8, 9 ) each have an evaluation circuit for detection of the phase and amplitude of the respective signal element.

This application is the U.S. National filing of InternationalApplication PCT/EP2006/006865, filed Jul. 13, 2006.

BACKGROUND

The invention relates to a multichannel radio-frequency receiver.

In radio-frequency receivers for radar systems, communicationappliances, test equipment and the like, the dynamic range is limited bythe electronic components that are used, and in the case of digitalprocessing in particular the analogue/digital converters that are used.

In order to increase the dynamic range, it is known from GB 2 204 200 Afor a received radio-frequency signal to be matched to the dynamic rangeof the components that are used by variable amplification afterconversion to an intermediate frequency followed by conversion to abaseband frequency, by means of automatic gain control (AGC). However,the variable gain adversely affects the signal quality. In order to makeit possible to react to rapid changes in the signal strength, the usefulsignal must also be delayed with respect to the actuating signal since,otherwise, the automatic gain control cannot carry out the controlprocess before the useful signal arrives at an assembly which limits thedynamic range. This can be achieved only with a great amount ofcomplexity. Finally, the gain setting of the AGC must be knownaccurately for calibration of measuring radars, in particularmeteorological radars.

As an alternative to automatic gain control, EP 0 660 539 B1 proposesthat a signal be split into three channels after the radio-frequencysignal has been converted to an intermediate frequency. One channel hasan amplifier and is supplied to one input of a multiplexer, a furtherchannel is supplied without any change to a further input of themultiplexer, and the last channel has a detector for the signal strengthand is connected to a control input of the multiplexer in order to passon either the amplified channel or the unamplified channel to a commonevaluation circuit for the signal, depending on the signal strength.However this requires an additional channel which is not used in thesignal evaluation and, furthermore, reduces the signal strength on theother two channels. In addition, the multiplexer corrupts the signalthat is passed on to the evaluation circuit, in particular duringswitching, so that the known receiver is not suitable for signals inwhich weak amplitudes frequently alternate with strong amplitudes.Finally, the components upstream of the signal divider must be designedfor the entire dynamic range of the receiver, and are therefore subjectto compromise.

SUMMARY

The invention is therefore based on the object of providing amultichannel radio-frequency receiver that allows better-qualityevaluation, with a simplified design.

This object us achieved in a multichannel radio-frequency receivercomprising a radio-frequency analogue section which has an input for anelectrical signal of a receiving device, a signal divider to split theelectrical signal into a plurality of signal elements according to apre-established division ratio and pass the signal elements to arespective plurality of channels. A lower-frequency section is connecteddownstream from the radio-frequency analogue section and has alower-frequency processing path in each of the channels for therespective signal elements received from the radio frequency section. Arespective evaluation circuit is provided for the signal elementreceived in each channel from the lower-frequency section, fordetermining the phase and amplitude.

This results in a multichannel radio-frequency receiver in which asignal divider for splitting a radio-frequency analogue electricalsignal from a receiving device such as a radar antenna or a testequipment head into signal elements which can be supplied toradio-frequency analogue channels is actually provided in aradio-frequency analogue section downstream from each of which channelsof a lower-frequency section of the radio-frequency receiver are in eachcase connected and each have an evaluation circuit for detection of thephase and amplitude of the respective signal element.

In the simplest case, all the sections which follow the signal dividerare designed identically. This makes it possible to achieve a furthercost reduction.

The splitting of the signal in the radio-frequency area itself betweenchannels which are used exclusively for signal processing and evaluationallows optimum use of the available signal strength, as well as optimumdesign, without any compromises, of all the signal-processing, and inparticular signal-evaluating components of the receiver, depending onthe signal strengths to be evaluated in the respective channels. Noise,signal distortion and other signal corruption are therefore minimized.

It is possible to provide for the signal to be split info signalelements even before the first amplification process. This results in afurther evaluation improvement.

It is possible to provide for a signal limiter to be connecteddownstream from the signal divider. This makes it possible to block orlimit signals which are too strong for one channel or for a plurality ofchannels. The only signals which are preferably passed on for processingon a channel are those which do not overdrive the components in thatchannel. In addition to protecting the channels against overvoltagedamage, the use of a signal limiter also makes it possible to detectsignals on other channels during a blind time on one channel. The blindtime is the time which a gas-discharge-based signal limiter requires inorder to quench gas-discharge paths, and is normally longer than atransmission pulse from a radar apparatus. In radio-frequency receiverswith an input signal limiter on the input side which blocks the entireradio-frequency receiver, it is therefore possible to avoid theoccurrence of so-called blind spots or blind rings.

It is possible to provide for a plurality of signal dividers to beconnected in series, in the form of a cascade, in order to scale thedynamic range virtually indefinitely.

It is possible to provide for a signal limiter to be connecteddownstream from the signal divider, and for a further signal divider tobe connected downstream from the signal limiter. This makes it possibleto use a single signal divider to protect a plurality of channels.

It is possible to provide for a frequency converter for converting therespective radio-frequency signal element to a signal element at anintermediate frequency to be provided in the lower-frequency section ineach channel. The signal elements can be processed at theintermediate-frequency level using simple means and with high quality.

It is possible to provide for the evaluation circuits to be matched tothe respective signal strength, with the matching being carried out inparticular by the choice and design of the components used. The matchingis then carried out by the division ratio of the signal or by thechannels having permanently set different gains, or by both.

It is possible to provide for the evaluation circuits each to have adigital/analogue converter for digitizing the respective signal element.This allows independent digital further processing for each channel, inparticular using a signal processor or computer.

It is possible to provide for the evaluation circuits each to have ademodulator. This allows independent processing for each channel.

The radio-frequency receiver may be designed for radio-frequencyelectromagnetic waves including the microwave range, or only themicrowave range, and in particular for a radar device, for example aweather radar device.

The signal strength in this case optionally refers to the maximumamplitude or the maximum intensity of the signal.

Further refinements of the invention can be found in the followingdescription and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail in the following textwith reference to exemplary embodiments which are illustrated in theattached figures.

FIG. 1 shows a block diagram of a radio-frequency receiver.

FIGS. 2, 3 and 4 illustrate signal elements at respectively differentpoints in the radio-frequency receiver shown in FIG. 1.

FIG. 5 shows a block diagram of a radio-frequency receiver having signaldividers connected in series in the form of a cascade.

FIGS. 6, 7 and 8 illustrate signal elements at respectively differentpoints in the radio-frequency receiver shown in FIG. 5.

FIG. 9 shows a block diagram of a further radio-frequency receiver.

DETAILED DESCRIPTION

The radio-frequency receiver 1, which is illustrated in a simplifiedform in FIG. 1, has a radio-frequency analogue section 2 with an input 3for an analogue, radio-frequency, electrical signal of a receivingdevice 4, for example in the form of a parabolic antenna for anelectromagnetic radar beam at a wavelength in particular in themicrowave range, having a signal divider 5 and having two channels 6 a,7 a. An analogue intermediate-frequency section 8 with channels 6 b, 7 bfollows the radio-frequency section 2. Finally, a digitalbaseband-frequency section 9 with channels 6 c, 7 c and outputs 10 fordata signals which correspond to the analogue radio-frequency electricalsignal, in particular in amplitude and phase, follows the analogueintermediate-frequency section 8.

The expediently passive signal divider 5 is, for example, a directionalcoupler and in this case splits the signal received from the input 3into two possibly in-phase signal elements with the same or a differentsignal element strength, which are each processed separately in thechannels 6, 7. If required, more than two signal elements and acorresponding number of channels are provided.

The dynamic range of the channels 6, 7 is in this case limited inparticular by the dynamic range of the respective analogue/digitalconverters 11 and, to the extent described, the signal divider 5 isarranged upstream of low-noise amplifiers 12, as well as by theirdynamic range. In order to widen the dynamic range in comparison tosingle-channel evaluation, the channels 6, 7 are designed forrespectively different signal strengths such that the dynamic range ofthe respective analogue/digital converter 11 and, if appropriate,low-noise amplifier 12 is used optimally. The channels 6, 7 can bedesigned for different signal strengths by suitable choice of thedivision ratio of the signal divider 5 and/or the gain of low-noiseamplifiers 12, 13 provided in the channels. By way of example, thefollowing text is based on the assumption that the aim is to process lowsignal strengths in the channel 6, and high signal strengths in thechannel 7.

The division ratio, which can be predetermined by the configuration ofthe signal divider 5 and may additionally be variable, is, for example,3:1, that is to say the strength of the signal element in the channel 6a is three times the strength of the signal element in the channel 7 aand three quarters of the strength of the undivided signal, while thestrength of the signal element in the channel 7 a is one third of thestrength of the signal element in the channel 6 a, and one quarter ofthe strength of the undivided signal. The maximum signal elementstrength K_(max) and G_(max) of the signal elements in the channels 6 aand 7 a, respectively, for the maximum permissible signal strengthS_(max) at the input 3 is illustrated in FIG. 2. Other division ratios,in particular 1:1, are likewise possible and may be combined withfurther gain ratios, with the gain ratios expediently being different ifthe division ratio is 1:1.

The low noise amplifiers (LNA) 12 which are in each case connected inthe radio-frequency section downstream from the signal divider 5 in thechannels 6 a, 7 a have different gains in this case. The amplifier 12 inthe channel 7 a for high signal strengths has to provide less gain thanthe amplifier 12 in the channel 6 a. The maximum signal strengthsK′_(max) and G′_(max) of the amplified maximum signal elements thatoccur are illustrated in FIG. 3, with the magnitude ratios beingdistorted in comparison to FIG. 2, because the gain is expedientlyseveral orders of magnitude. Instead of or in addition to the amplifiers12, a low-noise amplifier can be provided upstream of the signal divider5. However, it is particularly advantageous to use identical gains inthe channels, in order to allow the channels to be designed with thesame circuitry at low cost, in which case the signal divider is thenresponsible for splitting the signal strengths expediently between thechannels.

A mixer 14 is provided at each of the junctions between the channels 6a, 7 a of the radio-frequency section 2 and the downstream channels 6 b,7 b of the intermediate-frequency section 8, and converts theradio-frequency signal elements to an intermediate frequency, using thefrequency of an oscillator 15. The signal elements which have beenconverted to the intermediate frequency are amplified by furtherlow-noise amplifiers 13, whose gain ratios may be different. The maximumsignal strengths K″_(max) and G″_(max) of the signal elements which havebeen amplified by the amplifiers 13 are illustrated in FIG. 4, with themagnitude ratios being distorted in comparison to FIG. 3, because thegain is expediently several orders of magnitude.

At the junction between the channels 6 b, 7 b of theintermediate-frequency section 8 and the downstream channels 6 c, 7 c ofthe baseband-frequency section 9, the digital/analogue converters 11,which are clocked by an oscillator 16, digitize the respective signalelements and pass digital signals to demodulators 17, which are likewiseconnected to the oscillators 16. The division ratio of the signaldivider 5 and/or the gain of at least one amplifier 12, 13 are/isexpediently designed such that the maximum signal element strengthG″_(max) in the channel 7 for strong signals makes optimum use of thedynamic range D of the analogue/digital converters 11, while the maximumsignal element strength K″_(max) in the channel 6 for weak signalsconsiderably exceeds the dynamic range D, see FIG. 4. The circuitry isexpediently designed such that a signal element in the channel 7 forstrong signals can be processed and in particular digitized completelyin the channel 6 for weak signals with a signal element strength below athreshold value A, at which a predetermined resolution can still beachieved, see FIG. 4.

For this purpose, the amplifiers 12, 13 can provide linear amplificationor, in particular, non-linear amplification, for example logarithmicamplification, such that the region above the threshold value A in thechannel 7 and the region below the threshold value A in the channel 6are amplified more strongly than the respective other region, in orderto stretch the respective region of interest, for more accuratedigitizing.

The demodulators 17 determined the amplitude and phase of the respectivesignal element. Known I/Q demodulators can be used for this purpose. Thedemodulators 17 are expediently implemented by a digital signalprocessor or a computer program in a computer connected downstream fromthe analogue/digital converters 11. The computer may also be amicrocontroller, an ASIC for example in the form of an FPGA or EPLDetc., or a digital signal processor or the like, in which case thesoftware can be implemented as firmware.

The demodulators 17 are followed by a selection device 18 to whose inputside the digital values of, for example, the amplitude and phase of thesignal elements in the channels 6 c, 7 c are supplied and which producesoutput signals at the outputs 10. In the simplest case, the selectiondevice 18 selects that signal element which makes best use of thedynamic range to be output at the outputs 10, that is to say the signalelement whose signal strength comes closest to the dynamic range D,without exceeding it. It is also possible to provide for the selectiondevice 18 to identify those channels which are saturated. Furthermore,the phase differences and/or amplitude differences between the channels6 c, 7 c can be measured, in particular during a measurement and/orcalibration time period, in order to correct the measured values on thebasis of the differences during subsequent operation. The selectiondevice 18 is expediently implemented together with the demodulators 17as a computer program.

Instead of being followed by the intermediate-frequency section 5 asillustrated in FIG. 1, the radio-frequency section 2 can also befollowed by some other lower-frequency section. In particular, thelower-frequency section may have a plurality of series-connectedintermediate-frequency sections, no intermediate-frequency section butonly one baseband-frequency section (zero-IF receiver, see FIG. 9) or asection with analogue/digital converters to the intermediate frequencyor baseband frequency. Furthermore, analogue I/Q demodulators can beprovided instead of the analogue/digital converters, with the componentsin the channels being designed for their dynamic range.

In the radio-frequency receiver illustrated in FIG. 5, the signaldivider 5 is followed by signal dividers 19 in the form of a cascade, inorder to split the signal between four channels 6, 7, 20, 21 forgraduated signal strengths. Channel 6 is intended for the lowest signalstrength, while channel 21 is intended for the highest signal strength.The maximum signal element strengths G_(max), H_(max), I_(max), K_(max),corresponding to the respective channels 21, 20, 7, 6 after division,G′_(max), H′_(max), I′_(max), K′_(max) after amplification by theamplifiers 12 and G″_(max), H″_(max), I″_(max), K″_(max) afteramplification by the amplifiers 13 are illustrated in FIGS. 6 to 8,which correspond to FIGS. 2 to 4. In this case, the division ratio ofthe signal dividers 19 is 1:1, so that the signal element strengthsG_(max), H_(max), and I_(max), K_(max) are each the same. The componentsare designed such that a signal at the input 3, which leads to anamplified signal element with a signal strength at the threshold valueA, B or C as illustrated in FIG. 8, has a signal element strength in thechannels 20, 7 or 6, respectively, which is just below the dynamic rangeD of the respective analogue/digital converter 11.

Furthermore, by way of example, a signal limiter 22 is provided forchannels 6, 7 in FIG. 5. The signal limiter 22 prevents a signal with astrength which is above the greatest maximum permissible strength forthe subsequent channels, that is to say in this case which is above themaximum permissible strength for the channel 7, being passed through,while the signals with a strength which can be processed in channel 6 orchannel 7 are passed through. Signal limiters can also be providedindividually for individual channels, expediently in each case upstreamof the first amplifier in the respective channel. This makes it possibleto effectively prevent components being damaged as a result ofoverdriving or voltage spikes, since the only signals which are passedthrough are those which can be processed in the downstream channel orthe downstream channels. For example, the signal limiter 22 passes ononly signal elements with a strength which is within the dynamic range Dof the channel 7 after amplification. While the signal limiter 22 isworking, signal detection is still possible on the other channels, whichare designed for higher signal strengths and have no signal limiters, orno signal limiters which limit a signal element at the same time.

The embodiment as illustrated in FIG. 9 of a radio-frequency receiver 1in the form of a so-called zero-IF receiver comprises a radio-frequencysection 2 which is followed, directly via mixers 14, by alower-frequency section, for example a baseband-frequency section 9,with A/D converters 11. In this case, demodulation is carried outquasi-directly from the radio-frequency section 2, without anyintermediate-frequency section. Two mixers 14 are provided for thispurpose in each channel, are fed with a phase shift of 90° from theoscillator 15 and carry out the demodulation process together with theA/D converters 11, two of which are likewise provided for each channel,in order in this case to separately supply I/O data to the inputs of theselection apparatus for each channel, as in the case of the demodulator17 shown in FIG. 1.

1. Multichannel radio-frequency receiver comprising: a radio-frequencyanalogue section which has an input for an electrical signal of areceiving device, a signal divider to split said electrical signal intoa plurality of signal elements according to a pre-established divisionratio and pass the signal elements to a respective plurality ofchannels; a lower-frequency section connected downstream from theradio-frequency analogue section and having a lower-frequency processingpath in each of said channels for the respective signal elementsreceived from the radio frequency section; and a respective evaluationcircuit for the signal element received in each channel from thelower-frequency section, for determining the phase and amplitude. 2.Receiver according to claim 1, wherein a first amplifier is connecteddownstream from the signal divider in a signal path from the input to anoutput of the receiver.
 3. Receiver according to claim 1 wherein asignal strength limiter is connected downstream from the signal divider.4. Receiver according to claim 1, wherein a plurality of signal dividersare connected in series, in the form of a cascade.
 5. Receiver accordingto claim 1, wherein a signal strength limiter is connected downstreamfrom the signal divider, and a further signal divider is connecteddownstream from the signal limiter.
 6. Receiver according to claim 1,wherein the lower-frequency section in each channel has a frequencyconverter for converting the respective radio-frequency signal elementto a signal element at an intermediate frequency.
 7. Receiver accordingto claim 1, wherein the evaluation circuits can be matched to therespective signal strengths.
 8. Receiver according to claim 1, whereinthe evaluation circuits each have a digital/analogue converter fordigitizing the respective signal element.
 9. Receiver according to claim1, wherein the evaluation circuits each have a demodulator.
 10. Receiveraccording to claim 1, wherein the receiving device is a microwavereceiving device.
 11. Receiver according to claim 1, wherein thereceiver is a receiver for a radar device.
 12. Receiver according toclaim 1, wherein in each channel, a first amplifier is connecteddownstream from the signal divider in a signal path from the input to anoutput of the receiver; and the lower-frequency section in each channelhas a frequency converter for converting the respective radio-frequencysignal element to a signal element at an intermediate frequency. 13.Receiver according to claim 12, wherein the evaluation circuits eachhave a digital/analogue converter for digitizing the respective signalelement.
 14. Receiver according to claim 13, wherein the evaluationcircuits each have a demodulator.
 15. Multichannel radio-frequencyreceiver comprising: a radio-frequency analogue section which has aninput for an electrical signal of a receiving device, a signal dividerto split said electrical signal into a plurality of signal elementsaccording to a pre-established division ratio and pass the signalelements to a respective plurality of channels; a lower-frequencysection connected downstream from the radio-frequency analogue sectionand having a lower-frequency processing path in each of said channelsfor the signal elements received from the radio frequency section; meansfor amplifying all the signal elements in at least one of theradio-frequency section and lower-frequency section, whereby eachdivided and amplified signal element has different strength; arespective evaluation circuit for the signal element received in eachchannel from the lower-frequency section, each evaluation circuit havinga respective dynamic range for determining the phase and amplitude ofthe respective divided, amplified and processed signal element andgenerating a respective evaluation signal; and a selection deviceoperatively associated with all the evaluation circuits, for selectingas a receiver output, one evaluation signal having the divided,amplified and processed signal strength coming closest to the dynamicrange of its evaluation circuit.
 16. Receiver according to claim 15,wherein the signal divider splits said input signal equally and themeans for amplifying all the signal elements, amplifies said dividedsignals with different gains in each channel.
 17. Receiver according toclaim 15, wherein the signal divider splits said input signal unequallyand the means for amplifying all the signal elements, amplifies saiddivided signals with the same gain.
 18. Receiver according to claim 15,wherein a signal strength limiter is connected downstream from thesignal divider.
 19. Receiver according to claim 15, wherein thelower-frequency section in each channel has a frequency converter forconverting the respective radio-frequency signal element to a signalelement at an intermediate frequency.
 20. Receiver according to claim19, wherein the evaluation circuits each have a digital/analogueconverter for digitizing the respective signal element and ademodulator.